This invention relates to a color image clamshell type forming apparatus such as a color printer, a color copier and the like. More particularly it relates to a color image forming apparatus which can be easily maintained and which can stably form color images by adopting a process cartridge including image forming units.
A conventional color image forming apparatus in which a transfer drum is used, is disclosed in Japanese Patent Publication Open to Public Inspection No. 123257/1986. In the color image forming apparatus described therein, a color image is formed as follows: a document image is read out; a latent image is formed on a photoreceptor by laser beams which were modulated by obtained from said document image digital signal; the latent image is developed by a rotary type of color developing unit; and the thus obtained toner images are superimposed on each other on a transfer paper which is wound around a transfer drum so that a color image can be formed on the paper. Since the photoreceptor drum, the rotary type of developing unit, the transfer drum, and the like are individually provided to the apparatus in this case, the size of the apparatus becomes large as a whole and furthermore it is difficult to replace parts for maintenance work and to remove jammed paper when jamming has occurred in the apparatus.
In order to solve the problem explained above, a transfer drum type of color image forming apparatus has been proposed in Japanese Patent Publication Open to Public Inspection No. 72159/1983, which has a process cartridge to which a photoreceptor drum, a charger, a plurality of developing units, a cleaning unit, and the like are integrally provided.
In this prior art, the image forming units are provided in the process cartridge which can be easily attached to and removed from the apparatus, so that the image forming units can be replaced as required. Accordingly, the quality of the color images formed by this prior art apparatus was stabilized. The apparatus was compact, and the weight of the apparatus was decreased.
However, the color image forming apparatus disclosed in the above-described Japanese Patent Publication Open to Public Inspection No. 72159/1983, is provided with a plurality of thin developing units which are stacked horizontally. Consequently, the apparatus has the following disadvantages: the developer can not be sufficiently stirred in the developing unit and accordingly triboelectric charging is not fully sufficient; mixing of color toner tends to occur between adjacent developing units; and the quality and resolving power of a color image are deteriorated. As the image transfer means including the transfer drum is located under the photoreceptor drum, the cleaning unit and a plurality of developing units, the image tends to be contaminated by toner leaked from the cleaning unit and the developing units so that the image quality is further deteriorated.
In the color image forming apparatus described above, the image forming units and the transfer drum are separately removed when jamming occurs. Therefore, a large space is needed to remove the image forming units and the transfer drum, and furthermore repositioning is troublesome when this removed apparatus is re-attached to the apparatus.
A first object of the present invention is to provide a color image forming apparatus which can stably form a color image of high quality and which can be made compact.
A second object of the present invention is to provide a color image forming apparatus which can stably form a color image of high quality, and which can be made compact and can be easily maintained as the image forming units, the transfer drum and the like are integrally assembled into a compact cartridge.